It is known, in particular from patent document FR 2 932 409, to fabricate such a rod by using a mandrel on which one or more layers of carbon fibers are braided in radial superposition on one another.
That assembly is then installed in a mold in order to inject resin into the various layers carried by the mandrel prior to polymerizing the resin, e.g. by heating it, thereby constituting a rigid blank for a rod, which blank can be machined at its interfaces in order to form lugs therein.
The braiding of the layers of reinforcing fibers is then performed with a braiding installation as shown in FIG. 1, where it is referenced 1. The installation essentially comprises a ring 2 extending in a vertical plane, with the central axis AX of the ring thus being horizontal. The ring 2 carries a set of reels 3 carrying reinforcing fibers, the fibers converging on a region that is situated on the axis AX and that is offset from the plane of the ring.
When the braiding cycle is started, the mandrel, referenced 4, is moved along the central axis AX so as to pass through the ring 2 beyond the point where the fibers converge. Simultaneously, the reels carried on the ring 2 by motor-driven movable supports are actuated so as to reel out fibers in order to fabricate a sock of reinforcing fibers on the outside face of the mandrel 4.
Once the mandrel has passed right through the ring, i.e. once it is situated beyond the fiber convergence point, it is covered over its entire length by the sock.
The layer of reinforcing fibers is then cut between the mandrel and the ring, and the mandrel is removed and then put back behind the ring in order to pass through it once more so as to form a second layer of reinforcing fibers that is superposed radially on the first.
Thus, as shown diagrammatically in FIG. 2, it is possible to fabricate a general structure comprising the mandrel in its central region, which mandrel forms a support for two or more layers of braided fibers 6, 7 that extend all around the mandrel, over its entire length.
Specifically, as shown in FIG. 3, a braided layer comprises firstly interlacing fibers 8 and 9 that are inclined, e.g. at about 30°, on either side of the axis AX, and secondly longitudinal fibers 10 that are parallel to the axis AX, and that are held in position by the interlacing fibers 8 and 9 that interlace them.
In practice, and as can be seen in FIG. 3, each layer of braided fibers is made up of a plurality of sublayers, levels, or thickness, each comprising a series of longitudinal fibers 10 situated beside one another in a comb arrangement. The interlacing fibers 8, 9 interlace the longitudinal fibers 10 of the various sublayers together so as to form a coherent whole.
When the layers of braided fibers have been applied on the mandrel, the longitudinal fibers 10 of each sublayer are distributed uniformly about the mandrel 4 that carries them, i.e. they are regularly spaced apart from one another around the mandrel 4, as shown diagrammatically in FIG. 4.
In service, such a mechanical member is subjected to mechanical loading circumstances that are relatively complex, and as a result it is subjected to stresses that differ from one region of the member to another.
With a member fabricated by braiding, that situation leads to selecting the thickness of reinforcing fibers for depositing over the entire mandrel as a function of the maximum stress to which the member is to be subjected, even though the maximum stress actually corresponds only to a particular region of the member under consideration.
It follows that in many of its zones, the member is thus overdimensioned, thereby pointlessly penalizing the total weight of the member.